Calutron ion source



June 2, 1959 F. F. OPPENHEIMER 2,889,462

CALUTRQN ION SOURCE Filed July 23, 1946 MAGNETIC FIELD MAGNETIC FIELD INVENTOR FRA/v/r f. OPPf/Vfi/f/MER BY ATTORNEY United States CALUTRON ION SOURCE Frank F. Oppenheimer, Berkeley, Calif., assignor to the United States of America as represented by the United States Atomic Energy Commission Application July 23, 1946, Serial No. 685,643 4 Claims. (Cl. 250-413) This invention relates to calutrons and more particularly to a shielding structure for eliminating oscillating electrons in the ion source region of a calutron. Calutrons have been described in general in Atomic Energy for Military Purposes by H. D. Smyth and described in greater detail in the copending application of Ernest 0. Lawrence, Serial No. 557,784, filed October 9, 1944, which later issued as U.S. Patent No. 2,709,222 on May 24, 1955. They have been extensively employed and very successfully employed in the separation of the isotopes of the element uranium. In general, they include an ion generator from which ions are withdrawn by a powerful electric field and accelerated into a magnetic field. Thereafter the ions travel in curved paths, the ions of greater mass describing flatter curves than the ions of lighter mass. Appropriate collectors are placed across the various paths and the ions are neutralized and collected, each collector holding isotopes that are substantially separated from the isotopes found in the original charge material.

The entire calutron apparatus is enclosed in a vacuum tank which is disposed within the magnetic field which permeates the various structures inside of the vacuum tank. The vacuum in the tank is held at a desirable level, such as 10- or 10 mm. Hg. This pressure, however, leaves sufiicient gas particles within the vacuum tank so that when the ion beams are accelerated, they strike these gas molecules and ionize them in turn, generally forming a positive ion and a free electron. These free electrons are subjected to the crossed electric and magnetic fields found in the ion source region of a calutron and tend to oscillate violently along the magnetic field. These oscillating electrons not only ionize additional gas and multiply their eliect, but also interfere with the ion beam itself, causing flurries in the beam which are very undesirable, interfering severely with the separation work.

It is therefore an object of the invention to suppress or otherwise eliminate the oscillation of electrons in the space between the ion generator and the accelerating electrode of a calutron ion beam source.

Another object of the invention is to provide a preselected electric field surrounding the ion generator of a calutron of the type employing an ion generator maintained at a high positive potential.

Other objects and advantages of the invention will be apparent in the following description and claims taken in conjunction with the accompanying drawing forming a part of this specification, in which:

Figure 1 is a sectional view through the vacuum tank of a calutron and taken along the magnetic field showing an ion generator and an accelerating electrode indicating the equipotential lines; and

Fig. 2 is a view similar to Fig. 1 except that the ion generator is equipped with shields made particularly in accordance with the invention and further showing the equipotential lines existent around such shields.

As previously mentioned, ions are accelerated by use of an intense electric field. It is obvious that this electric 2,889,462 Patented June 2, 1959 field may be set up either by having the ion generator at ground potential and the accelerating electrode at a high negative potential or by having the ion generator at a high positive potential and the accelerating electrode at ground potential. This latter system, that is, the ion generator at a high positive potential, is preferred inasmuch as it eliminates the need for an electric tube through which the electron beam may pass to the collectors. In this connection, it is noted that the vacuum tank in which the various calutron elements are disposed is normally maintained at ground potential for the safety of the operators.

Referring now to Fig. 1, there is illustrated a portion of a vacuum tank 10 having an insulator 11 secured to an inner wall thereof and having an ion generator 12 supported on the inner end of the insulator. Appropriate electrical leads (not shown) maintain the ion generator 12 at a high positive potential. The ion generator 12 has an ion exit opposite which is disposed an accelerating electrode 13 having a slotted passage 14 therethrough, as indicated by the dotted lines. The accelerating electrode 13 and the vacuum tank to which it is secured are maintained at ground potential, creating a high negative electric field between the electrode 13 and the ion generator l2. This electric field attracts the positive ions from the ion generator, accelerating them so that as they pass through the electrode 13, they travel in the curved paths mentioned previously. This ion beam is represented by the arrows 15. The direction of the magnetic field permeating the entire structure is shown by a flux line 16. The equipotential lines existent between the ion generator 12 and the grounded structures about it are indicated by the lines 17.

After the ions are accelerated by the electric field indicated by these lines, they bombard residual gas within the vacuum tank 10, ionizing it and creating positive ions and free electrons. These electrons that are generated in the space between the ion generator 12 and the electrode i3, being negative particles, are attracted toward the highly positive ion generator 12. The intense magnetic field, however, prevents them from travelling in a straight line, causing them to follow curved paths in a very tight circle. Further, inasmuch as the equipotential lines surrounding the top and bottom of the ion generator 12 are curved and the electrons are substantially confined to the flux lines 16, the electrons are repelled by the outermost equipotential lines 17 because these lines are more negative. They are then projected downwardly along the magnetic flux lines until they strike the curved lines at the bottom of the ion generator 12 whereupon they are again repelled shooting past the ion generator to the topside again. This alternate repulsion, together with the inherent attraction associated with the curved equipotential lines, sets the electrons in violent oscillation along the magnetic field while they slowly progress toward the ion generator 12. These oscillating electrons interfere with the ion beam 15 causing it to become fiurried and irregular.

Fig. 1 therefore represents the prior art devices in which the electrons in the space between the ion generator 12 and the accelerating electrode 13 are in violent oscillation. Fig. 2, however, shows the same ion generator 12 of Fig. 1 equipped with shielding in accordance with my invention. This shielding comprises essentially plates 18 made of a metallic conductor and electrically and mechanically connected to the ion generator 12. These shields 18 intercept the magnetic flux lines 16 that pass between the ion generator 12 and the accelerating electrode 13, and set up a new curvature for the equipotential lines 17 in this region. When the electrons are now freed in the region of the accelerating gap, they no longer encounter a repelling force at the top and bottom of .,the.ion,generator 12. Instead, as they travel along the flux lines 16, they find that the equipotential lines 17 at the upper and lower ends of the ion generator 12 attract the electrons. because of the fact 1 that I the further toward the plates'18 that'the electronstraveL-the more positive are the equipotential lines.- The electrons are therefore accelerated toward the plates 18 and impinge and. discharge thereon. This shielding, therefore, not only suppresses the oscillation ofthe electrons but actually removes them from the region, eliminating any harmful effect that their presence may have.

Although this invention has been described with reference to a particularembodiment thereof, it is notlirnited to this embodiment nor otherwise except by the terms of the following claims.

What is claimedis:

l. A calutron comprising means for establishing a magnetic. field, a vacuum tank disposed therein and maintained at a potential, an ion generator mounted within the: tank and maintained at a potential positive with respect to the tank, an accelerating electrode disposed adja cent the ion generator and maintained at a potential negative with respect to the ion generator, and plates secured on opposite ends of the ion generator along the magne ic field and intercepting a portion of the magnetic field between the ion generator and the accelerating electrode and maintained at the potential of the ion generator.

2. A calutron comprising means for establishing a magnetic field, a vacuum tank disposed therein and maintained at ground potential, an ion generator mounted within the tank and maintained at a potential positive with respect to the tank, an accelerating electrode placed adjacent to the ion generator and maintained at a potential negative with respect to the ion generator, and magnetically transverse plates secured to the ion generator at opposite ends along the magnetic field and projecting toward but spaced from the accelerating electrode.

3. A calutron comprising means for establishing a magnetic field, a vacuum tank disposed therein and maintained at ground potential, an ion generator mounted within the tank and maintained at' a potential positive with respect to the tank, an acceleratingelectrode placed adjacent to the ion generator and maintained at ground potential, and magnetically transverse plates secured to the ion generator at opposite ends along the magnetic field and projecting toward but spaced from the accelerating electrode.

4. A calutron comprising means for establishing; a magnetic field, a vacuum tank disposed therein, anion generator disposed in the vacuum tank and maintained at a potential positive with respect thereto, an accelerating electrode disposed adjacent to the ion generator and maintained at a potential negative with respect thereto, and means for reversing the electric field curvature that is normally present in the region between the iongen-- erator and the accelerating electrode.

No references cited. 

